Metal can for a food product

ABSTRACT

A metal can ( 40 ) for preserving a food product sterilised by heat treatment after closing the can, is made up of an integral body forming the bottom ( 41 ) and the side wall ( 43 ) of the can, and a lid ( 42 ) are mounted on the body in order to seal the latter, the minimum thickness of the side wall ( 43 ) being between 20% and 60% of the thickness of the centre of the bottom ( 41 ). The height of the can ( 40 ) is between 1.5 and 3.5 times the width thereof, and the bottom ( 41 ) and/or the lid ( 42 ) of the can has a central wall ( 411, 421 ) with an outwardly convex shape, connected to the side wall ( 43 ) by a peripheral groove ( 410 ) opening up towards the outside.

1. FIELD OF THE INVENTION

The present invention relates to a metal can, for preserving a foodproduct sterilised by heat treatment after the closing of the can.

2. PRIOR ART

Traditionally, as shown in FIG. 1, the cans were formed by a rectangularsheet metal portion 10 folded and welded in such a manner to form abody, with a bottom 11 and a lid 12 formed of sheet metal platesassembled at both ends of this body. Such a can is called a “three-part”can, because it involves three separate elements welded or seamedtogether.

More recently, as shown in FIG. 2, cans have been produced by drawing asheet metal, called a flank, so as to form into a single integral body20 the bottom and the side wall of the can body. A lid 23 formed of asheet metal plate then permits to close this can. Such cans, whosebottom and side wall form a single part, are called “two-part” cans.

As shown in FIG. 3, which is a sectional view of the can of FIG. 2, suchcan has a variable thickness, according to the height in the can, withina range of +25% to −25% of the initial thickness of the flank.

Another drawing technology, commonly called DWI (“Drawn and WallIroning”) technology, has been developed, which makes it possible toform “two-part” cans whose side walls are ironed. FIG. 4 is a sectionalview of such a can 30. The thickness “e” of the centre of the bottom 31of this can is substantially equal to the thickness of the flank thathas been drawn. The thickness of the bottom is between +0% and −15% ofthis thickness “e”, as the shaping thereof is liable to locally cause aslight thinning. On the other hand, the thickness “e′” of the wall 33 isreduced down to 20% of the thickness “e” of the centre of the bottom.The lid 32 has the thickness “e″” of the sheet metal in which it hasbeen formed.

This DWI technology makes it possible to produce cans, hereinaftercalled “ironed-wall cans”, lighter in weight than the other types ofcan. Their characteristics make them advantageous for being used asbeverage-can, but they remain not very appropriate for being used ascans for food products. Indeed, the latter must be submitted, after theclosing thereof, to a sterilisation by heat treatment that inducepositive and negative variations of the internal pressure in the can.

The most often used ironed-wall cans, and in particular thebeverage-cans, are not adapted to such pressure variations. The use ofsuch cans for containing food products is consequently of littleinterest, and thus remains rare.

3. OBJECTS OF THE INVENTION

One object of the present invention is to overcome these prior artdrawbacks.

In particular, one object of the invention is to provide metal cans forpreserving a food product sterilised by heat treatment after the closingof the can, using an optimized quantity of material.

Another object of the invention is to provide such cans, whosesterilisation by heat treatment, after the closing thereof, isfacilitated and consumes a minimum quantity of energy.

The invention has also for object to make it possible to manufacture andeasily implement such cans, using at most material and elements that areidentical or similar to those used for the prior art cans.

4. DISCLOSURE OF THE INVENTION

These objects, as well as others, which will become more clearlyapparent hereinafter, are reached by a metal can, for preserving a foodproduct sterilised by heat treatment after the closing of the can, madeup of an integral body forming the bottom and the side wall of the can,and of a lid assembled to this body so as to close the latter, theminimum thickness of the side wall being between 20% and 60% of thethickness of the centre of the bottom, the height of the can being,according to the invention, between 1.5 and 3.5 times the width thereof,and preferably between 1.7 and 3 times, and the bottom and/or the lid ofthe can having a central wall with an outwardly convex shape, connectedto the side wall by a peripheral groove opening up outwards.

Such a can may be manufactured with an optimized quantity of material,and may be subjected to a sterilisation heat treatment without anydamage and consuming less energy than the prior art cans.

Preferentially, the internal pressure of the can is higher than theatmospheric pressure.

This characteristic, in combination with the other characteristics ofthe can according to the invention, contributes to the rigidity of thecan.

Advantageously, said peripheral groove has a first wall connected to theconvex central wall, a second wall connected to a peripheral area ofconnexion to the side wall of the can, and a bottom forming a roundedshape, and:

-   -   the first wall forms an angle between 2° and 45° with the axis        of the can,    -   the connexion between the first wall and the central wall forms        a rounded shape with a radius greater than 0.5 mm,    -   the depth of the groove is between 1 mm and 7 mm, and    -   the rounded shape of the bottom of the groove has a radius        smaller than 5 mm.

A bottom or a lid with such characteristics provides the can with a goodresistance to internal pressure.

According to an advantageous embodiment, the lid is made up of a disk ofsteel-based material, the can capacity is 212 ml, 425 ml or 850 ml, andto these capacities are associated lids of diameter 52 mm, 65 mm and 83mm, respectively.

According to an advantageous embodiment, the lid is made up of analuminium disk, the can capacity is 212 ml, 425 ml or 850 ml, and tothese capacities are associated lids of diameter 52 mm, 63.7 mm and 81.5mm, respectively.

These combinations of lid sizes and standard can volumes make itpossible to implement the invention, respecting the food packer needsand using the existing lids and seaming equipment.

According to an advantageous embodiment, beads are formed on the sidewall of the can so as to increase the resistance thereof to the externalpressure.

The present invention also relates to an integral body of a metal can,for preserving a food product sterilised by heat treatment after closingof the can, the body comprising a bottom and a side wall, the minimumthickness of the side wall being between 20% and 60% of the thickness ofthe centre of the bottom, the height of the body being, according to theinvention, between 1.5 times and 3.5 times the width thereof, andpreferably between 1.7 and 3 times, and the bottom having a central wallwith an outwardly convex shape, connected to the side wall by aperipheral groove opening up outwards.

This body makes it possible to manufacture a can such as describedabove.

Preferentially, the peripheral groove of this body has a first wallconnected to the convex central wall, a second wall connected to aperipheral area of connexion to the side wall of the can, and a bottomforming a rounded shape, and:

-   -   the first wall forms an angle between 2° and 45° with the axis        of the can,    -   the connexion between the first wall and the central wall forms        a rounded shape with a radius greater than 0.5 mm,    -   the depth of the groove is between 1 mm and 7 mm, and    -   the rounded shape of the bottom of the groove has a radius        smaller than 5 mm.

According to an advantageous embodiment, beads are formed on the sidewall of the body so as to increase the resistance thereof to theexternal pressure.

5. LIST OF FIGURES

Other purposes, advantages and characteristics of the invention willbecome more clearly apparent from the following description of apreferred embodiment, non-limitating of the object and scope of thepresent patent application, in connection with the appended drawings, inwhich:

FIG. 1 is a schematic view of the elements constituting a can of the“three-part” type according to the prior art;

FIG. 2 is a schematic view of the elements constituting a can of the“two-part” type according to the prior art;

FIG. 3 is a sectional view of the can of FIG. 2;

FIG. 4 is a sectional view of the ironed-wall can of the prior art;

FIG. 5 is a sectional view of a can according to an embodiment of theinvention.

6. DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

The “three-part” cans and the “two-part” cans produced by a conventionaldrawing process have a thickness that varies between +25% and −25% ofthe thickness of the flank used. To optimise the quantity of metalimplemented to manufacture such a can of a given capacity, the diameter“D” of the can is close to the height “h” thereof.

Therefore, standard sizes have been defined by the profession for thecans intended to contain food products, in particular by the standardsEN 13 025 to 13 029, implementing for example lids forming disks withthe following diameter:

-   -   99 mm for the cans of 850 ml capacity;    -   83 mm for the cans of 425 ml capacity;    -   65 mm for the cans of 212 ml capacity.

These sizes, which are conventionally used, make it possible to obtaincans with a diameter that does not differ by more than 20% from theheight thereof, with an optimised quantity of material.

Due to its low thickness, the side wall of the body of an ironed-wallcan does not have naturally a satisfying rigidity with respect to theexternal stresses.

A conventional technique to reinforce this rigidity consists in formingbeads on the body of the can to improve the resistance thereof to theside external pressure. However, these beads do not favour theresistance of the can to a vertical effort.

FIG. 5 is a schematic sectional view of a cylindrical can 40 accordingto a preferential embodiment of the invention. The side wall 43 of thiscan has been ironed with the “DWI” technology. Hence, the lowestthickness “e′” thereof is between 20% and 60%, and preferably between30% and 50%, of the thickness “e” of the middle of the bottom 41.

To reinforce the rigidity of this can, a substance is added to thecontent of the latter, before the closing thereof, which, whenvaporizing, produces an overpressure inside the can. This substance,which may be for example liquid nitrogen, has for effect to rigidify thepressurized can and to improve the resistance thereof both to the sideexternal pressure and to the vertical effort.

The cans for food products must, unlike the beverage-cans, be submittedto a sterilisation by heat treatment after the closing thereof. Suchsterilisation, which involves to heat the content of the can to atemperature of about 110° C. to 150° C. (preferably between 110 and135°), generates a pressure increase inside the can up to about 3 bars.Such increase is more important for the pressurized cans, in which thepressure may reach 5 bars.

Generally, the side wall of the can undergoes a very small deformationunder the effect of this pressure. Only the bottom and the lid get outof shape, and allow the expansion of the can, thus limiting the increaseof the internal pressure during the sterilisation process. For a canwith a given volume, the greater the size of the bottom and the lid, thegreater the possible expansion thereof.

The one skilled in the art was thus convinced up to now that, to undergoa heat treatment after the closing thereof, the ironed-wall cans had tohave a bottom and a lid with a great enough size with respect to theheight thereof. In practice, these cans have the common proportions ofthe cans containing food, whose diameter is close to the height.

As determined by the inventors, to optimise the quantity of metalimplemented to manufacture a pressurized ironed-wall can of a givencapacity, the height “h” of the can must be greater than the diameter“D” thereof. This height has thus to be between 1.5 and 3.5 times, andpreferably between 1.7 and 3 times, the diameter “D”.

Consequently, the conventional proportions of the cans intended tocontain food products did not make it possible, up to now, to optimizethe quantity of material of the ironed-wall cans. The one skilled in theart was led to think that the use of ironed-wall cans was of littleinterest for the food products.

The can 40 shown in FIG. 5 has a height “h” that is between 1.7 and 3times the diameter “D” thereof, which makes it possible to optimize thequantity of metal implemented for the manufacture thereof.

To permit the heat treatment of this can 40 without generating anexcessive internal pressure, the lid 42 and the bottom 41 have aparticular shape with a central wall, 421 and 411, respectively, havingan outwardly convex shape, connected to the side wall of the can by aperipheral groove, 420 and 410, respectively, opening up outwards. Thisparticular shape facilitates the elastic deformation of the bottom andthe lid in case of internal overpressure. Bottoms and lids of this typeare well known in themselves and are notably described in the documentEP 1 813 540.

The lid 42 thus has:

-   -   a central wall 421,    -   a peripheral area 422 for the seaming thereof with the side wall        43 of the can,    -   a peripheral groove 420, having a first wall 423 connected to        the central wall 421, a second wall 424 connected to the        peripheral area 422, and a bottom 425 forming a rounded shape.

In this lid 42, the first wall 423 forms an angle of about 45°, and inany case between 2° and 45°, with the axis of the can; the connexionbetween the first wall 423 and the central wall forms a rounded shapewith a radius greater than 0.5 mm; the depth of the groove 422 isbetween 1 mm and 7 mm; and the rounded shape of the bottom 425 of thegroove has a radius smaller than 5 mm.

Likewise, the bottom 41 has:

-   -   a central wall 411,    -   a peripheral area 412 of connection with the side wall 43 of the        can,    -   a peripheral groove 410, having a first wall 413 connected to        the central wall 411, a second wall 414 connected to the        peripheral area 412, and a bottom 415 forming a rounded shape.

In this bottom, the first wall 413 forms an angle of about 5°, and inany case between 2° and 45°, with the axis of the can; the connectionbetween the first wall 413 and the central wall 411 forms a roundedshape with a radius greater than 0.5; the depth of the groove 410 isbetween 1 mm and 7 mm; and the rounded shape of the bottom 415 of thegroove has a radius smaller than 5 mm.

The grooves 410 and 420 having these characteristics facilitate thedeformation of the bottom and the lid, respectively, of the can 40.Therefore, when the can 40 is heated during the heat treatment thereof,the increase of its internal pressure causes the temporary andreversible deformation of the bottom 41 and the lid 42, which increasesthe internal volume of the can. This volume increase makes it possibleto limit the effective pressure in the can 40 to values that do not riskdamaging it.

The lid 42 and the bottom 41 providing a better resistance to theinternal pressure, it is therefore possible to manufacture a pressurizedironed-wall can that can be sterilised by heat treatment, and whoseheight to diameter ratio can be chosen in such a way to optimize thequantity of material used.

In other possible embodiments of the invention, it is possible that onlythe lid, or only the bottom, is designed so as to exhibit a goodresistance to the internal pressure.

It is also to be noted that the invention is not limited to the shownbottom and lid profiles. Other profiles allowing the can to support highpressures can be implemented, as for example those described in thedocument EP 1 813 540.

The volumes of the cans are standardised, in particular by the standardsEN 13 025 to 13 029. The modifications of the can proportions in orderto optimize them have thus to be made, preferably, with keepingidentical volumes.

Moreover, the sizes of the can lids are also standardised. For the canmanufacturers, it is important to respect these standards because theapplication of the lids for the closing of the cans is not performed bythe can manufacturer but by the food packer that fills the can. The lidsused have thus to be adapted to the seaming machines used by the foodpackers.

To modify the can proportions of the cans without having to use lids ofnon-standardized diameters, it has been imagined by the inventors tosize the cans, for each standard capacity, in such a way that they canbe closed by the standard lids commonly used to close cans of lowercapacity.

Therefore, it is advantageous, for the cans closed with lids formed indisks of steel-based material, to use:

-   -   lids of 52 mm diameter for cans of 212 ml capacity,    -   lids of 65 mm diameter for cans of 425 ml capacity,    -   lids of 83 mm diameter for cans of 850 ml capacity.

For the cans closed by lids formed in disks of aluminium-based material,it is advantageous to use:

-   -   lids of 52 mm diameter for cans of 212 ml capacity,    -   lids of 63.7 mm diameter for cans of 425 ml capacity,    -   lids of 81.5 mm diameter for cans of 850 ml capacity.

These combinations make it possible to easily manufacture cans havingproportions close to the optimized proportions.

The cans having the characteristics of the invention can be heatsterilised more rapidly and using less energy than the prior art cans.Indeed, the proportions of these cans allow them to have a greatersurface of thermal exchange with the outside, which facilitates theheating thereof. Moreover, the thickness of food to be heated in the canis smaller, due to the small width of the latter. The side walls beingthinner, they better transmit the heat. Finally, the total quantity ofmetal material that is heated during the sterilisation of a can issmaller, which consumes less energy.

The cans having the characteristics of the invention may also have sizesthat make them adapted for a more efficient and more compact storage.Therefore, by way of example, a type of pallet that is used has a lengthof 1200 mm, a width of 800 mm, and the height thereof has to be between1000 and 1030 mm.

On such a pallet, it is possible to store 1860 conventional cans of 425ml, having a diameter of 73 mm for a height of 101.54 mm. These cans arestored into 10 layers of 186 cans. On the other hand, it is possible tostore 1960 cans of the same volume according to the invention, having adiameter of 65 mm for a height of 128.08 mm. These cans are then storedinto 8 layers of 245 cans. The invention thus makes it possible to place100 more cans on each pallet than in the prior art, i.e. 2400 more cansin a truck transporting 24 pallets. Consequently, it providessubstantial saving on the transportation costs.

It is to be noted that the lid size is not necessarily equal to thewidth of the can side wall. It is indeed possible to provide anecking-in at the top of this side wall, for the seaming of a lid havinga size that is smaller than the width of the wall. It is also possible,in some cases, to seam a lid having a size that is greater than thewidth of the can.

The present invention may be implemented for cans closed by lids with asize between 20 mm and 153 mm. However, it is preferably implemented forcans closed by lids having a size between 52 mm and 99 mm.

In a particular embodiment of the invention, it is possible to shape theside walls of the can in such a way to form therein beads for improvingthe resistance of the latter to the external pressure.

The present invention mainly applies to the cylindrical cans, thequasi-cylindrical cans, the cans with a polygonal (hexagonal, octagonal. . . ) cross-section, the cans whose side walls are slightly“barrel-shape” bulged, or the cans of different shapes liable to havethe same proportions.

The body of the cans, forming the bottom and side walls of the latter,is also within the scope of the present application, independently ofthe lid thereof, in particular if it has the characteristics allowing itto form a can according to the invention when associated with a commonlid that is not shaped so as to be deformable.

1. A metal can (40), for preserving a food product sterilised by heattreatment after the closing of the can, made up of an integral bodyforming the bottom (41) and the side wall (43) of the can, and of a lid(42) assembled to this body so as to close the latter, the minimumthickness of the side wall (43) being between 20% and 60% of thethickness of the centre of the bottom (41), characterized in that theheight of the can (40) is between 1.5 and 3.5 times the width thereof,and in that the bottom (41) and/or the lid (42) of the can (40) has acentral wall (411, 421) with an outwardly convex shape, connected to theside wall (43) by a peripheral groove (410, 420) opening up outwards. 2.A can (40) according to claim 1, characterized in that the internalpressure thereof is higher than the atmospheric pressure.
 3. A can (40)according to claim 1, characterized in that said peripheral groove (410,420) has a first wall (413, 423) connected to the convex central wall(411, 421), a second wall (414, 424) connected to a peripheral area ofconnexion to the side wall of the can, and a bottom (415, 425) forming arounded shape, and in that: the first wall (413, 423) forms an anglebetween 2° and 45° with the axis of the can, the connexion between thefirst wall (413, 423) and the central wall (411, 421) forms a roundedshape with a radius greater than 0.5 mm, the depth of the groove (410,420) is between 1 mm and 7 mm, and the rounded shape of the bottom (415,425) of the groove has a radius smaller than 5 mm.
 4. A can (40)according to claim 1, characterized in that the lid (42) is made up of adisk of steel-based material, in that the capacity thereof is 212 ml,425 ml or 850 ml, and in that to these capacities are associated lids ofdiameter 52 mm, 65 mm and 83 mm, respectively.
 5. A can according toclaim 1, characterized in that the lid (42) is made up of an aluminiumdisk, in that the capacity of the can is 212 ml, 425 ml or 850 ml, andin that to these capacities are associated lids of diameter 52 mm, 63.7mm and 81.5 mm, respectively.
 6. A can according to claim 1,characterized in that beads are formed on the side wall (43) thereof, soas to increase the resistance thereof to the external pressure.
 7. Anintegral body of a metal can (40), for preserving a food productsterilised by heat treatment after closing of the can, the bodycomprising a bottom (41) and a side wall (43), the minimum thickness ofthe side wall (43) being between 20% and 60% of the thickness of thecentre of the bottom (41), characterized in that the height of the bodyis between 1.5 times and 3.5 times the width thereof, and in that thebottom (41) has a central wall (411) with an outwardly convex shape,connected to the side wall (43) by a peripheral groove (410) opening upoutwards.
 8. An integral body of a can according to claim 7,characterized in that said peripheral groove (410) has a first wall(413) connected to the convex central wall (411), a second wall (414)connected to a peripheral area (412) of connexion to the side wall (43)of the can (40), and a bottom (415) forming a rounded shape, and inthat: the first wall (413) forms an angle between 2° and 45° with theaxis of the can, the connexion between the first wall (413) and thecentral wall (411) forms a rounded shape with a radius greater than 0.5mm, the depth of the groove (410) is between 1 mm and 7 mm, and therounded shape of the bottom (415) of the groove has a radius smallerthan 5 mm.
 9. An integral body of a can (40) according to claim 7,characterized in that beads are formed on the side wall (43) thereof, soas to increase the resistance thereof to the external pressure.
 10. Acan (40) according to claim 2, characterized in that said peripheralgroove (410, 420) has a first wall (413, 423) connected to the convexcentral wall (411, 421), a second wall (414, 424) connected to aperipheral area of connexion to the side wall of the can, and a bottom(415, 425) forming a rounded shape, and in that: the first wall (413,423) forms an angle between 2° and 45° with the axis of the can, theconnexion between the first wall (413, 423) and the central wall (411,421) forms a rounded shape with a radius greater than 0.5 mm, the depthof the groove (410, 420) is between 1 mm and 7 mm, and the rounded shapeof the bottom (415, 425) of the groove has a radius smaller than 5 mm.11. A can (40) according to claim 2, characterized in that the lid (42)is made up of a disk of steel-based material, in that the capacitythereof is 212 ml, 425 ml or 850 ml, and in that to these capacities areassociated lids of diameter 52 mm, 65 mm and 83 mm, respectively.
 12. Acan according to claim 2, characterized in that the lid (42) is made upof an aluminium disk, in that the capacity of the can is 212 ml, 425 mlor 850 ml, and in that to these capacities are associated lids ofdiameter 52 mm, 63.7 mm and 81.5 mm, respectively.
 13. A can accordingto claim 2, characterized in that beads are formed on the side wall (43)thereof, so as to increase the resistance thereof to the externalpressure.
 14. An integral body of a can (40) according to claim 8,characterized in that beads are formed on the side wall (43) thereof, soas to increase the resistance thereof to the external pressure.